Skip to main content

Full text of "Treatise On Applied Analytical Chemistry(Vol-1)"

See other formats

HEAVY OILS  (LUBRICATING OILS)                    357

lost by evaporation ; sufficient, however, remains for the saponification,
which takes place fairly rapidly (in about half an hour).

Without evaporating off all the alcohol, the contents of the flask are
poured into a separator and the flask thoroughly rinsed out, at first with
small quantities of alcohol and then with ether. Sufficient water is added
to dissolve the soap formed and sufficient ether to dissolve the mineral
oil. Tlie alkaline liquid is almost neutralised towards phenolphthalein by
means of acetic acid and shaken, a sharp division occurring on standing
between the ethereal layer containing the mineral oil and the soap solution.
The ethereal liquid is separated, washed with distilled water until the
alkaline reaction disappears, and distilled from a tared flask, the last traces
of ether being expelled in a current of air.

The residue is dried in an air-oven at 105 for an hour and weighed ;
the weight is multiplied by 20 and the product subtracted from 100, the
remainder being the percentage by weight of the fatty substance.

To determine the nature of the fatty matter, the soap solution is treated
with dilute sulphuric acid and the fatty acids collected and identified by
their colour reactions and their physical characters (see chapter on Fatty
Substances). If blown or oxidised oils have been added to the mineral
oil, the fatty acids are brown, have an odour of vegetable oils and are soluble
in ether, from which they are partially precipitated by petroleum ether ;
the precipitated part has a pitchy appearance. In some of their characters,
these fatty acids might be confused with those of fish oils, but the latter
have a quite different odour and are precipitated by Halphen's bromine
reagent (see Fish Oils), with which the fatty acids of oxidised oils give no

When it is necessary to examine the characters of mineral oil changed
by previous operations, the saponification is carried out in the cold as
follows :

In a separating funnel, 50 grams of the oil, 200 c.c. of light petroleum
ether and 200 c.c. of 10% alcoholic potash (in 95% alcohol) are vigorously
and frequently shaken for about four hours and then allowed to settle, the
ethereal layer being separated and washed several times by shaking with
cold water, and the petroleum ether evaporated on a water-bath. The
residue consists of the mineral oil; its freedom from fatty matter may be
ascertained by determining its saponification number, which should be
almost zero.

6. Detection of Alkaline and Alkaline-Earthy Soaps.i. QUALI-
TATIVE. The alkaline soaps may be dissolved by shaking the oil with
water, whilst the alkaline-earthy soaps are decomposed by shaking with
hydrochloric acid : in this way the bases pass into solution in the hydro-
chloric acid.

2. QUANTITATIVE DETERMINATION. About 10 grams of the oil are
weighed, dissolved in 50 c.c. of ether, and shaken in a separating funnel
with dilute hydrochloric acid, the ethereal solution being allowed to separate
and washed repeatedly with water; if the oil is sufficiently clear, alcohol
is added and the acidity determined, the fatty acids being deduced from
the result obtained (see Fatty Substances). If, however, the oil is too     IOO